This invention relates to the field of trigger activated rifles. More particularly it relates to an adjustable trigger mechanism for use in combination with the AK47 family of Rifles.
The Kalashnikov assault rifle, also known as the AK-47 (Avtomat Kalashnikova-47, Kalashnikov automatic rifle, model of 1947), and its derivatives, also known under the common name of AK, is the most prolific small arm of the 2nd half of the 20th century. It had been and still is (in more or less modified forms) manufactured in dozens of countries, and used in hundreds of countries and conflicts since its introduction. The total number of the AK-type rifles made worldwide during the last 50 years is estimated at 90+ millions. This is a true legendary weapon, known for its extreme ruggedness, simplicity of operation and maintenance, and unsurpassed reliability even in worst conditions possible. It is used not only as a military weapon, but also as a platform for numerous sporting civilian rifles.
The AKM is a gas operated, selective fire assault rifle. The gas operated action has a bolt carrier permanently attached to a long stroke gas piston. The gas chamber is located above the barrel. The bolt carrier rides on the two rails, machined in the receiver, with the significant clearances between the moving and stationary parts, allowing the gun to operate even when its interior is severely fouled with sand or mud.
The rotating bolt has two massive lugs that lock into the receiver. This bolt is so designed that on the unlocking rotation it also makes a primary extraction movement to the fired case. This results in a very positive and reliable extraction even with dirty chamber and cases. The rotation of the bolt is ensured by the curved cam track, machined in the bolt carrier, and by the appropriate stud on the bolt itself. The return spring and a spring guide are located behind the gas piston and are partially hidden in its hollow rear part when bolt is in battery. The return spring base also serves as a receiver cover lock. The cocking handle is permanently attached to the bolt carrier (in fact, it forms a single machined steel unit with carrier), and does reciprocate when gun is fired.
The receiver of the AKM is made from the stamped sheet steel, with machined steel inserts riveted into the place where required and houses the trigger mechanism. The relatively simple trigger/hammer mechanism features a hammer with two sears. A first or main sear mounted on the trigger extension. A second sear for the semi-automatic fire intercepts the hammer in the cocking position after the shot is fired and until the trigger is released.
The AKM trigger unit also featured a hammer release delay device, which is served to delay the hammer release in the full auto fire by few microseconds. This does not affect the cyclic rate of fire, but allows the bolt group to settle in the forward most position after returning into the battery. A combined safety and fire selector switch is located on the right side of the receiver and varies in operation as a safety to prevent fire of the weapon and also to allow semi and fully automatic operation by changing position.
While built to be a reliable performer even in dirty environments, the large tolerances built into the receiver mounted trigger assembly yield a trigger action that is loose, crude and lacks any components which would allow adjustement of the aspects of trigger pull to the individual marksman""s requirements. The trigger provided with conventional AK-47 rifles and its derivitives is a simple pull and shoot device where pulling the trigger activates the hammer which communicates with adjacent parts to fire the weapon. It lacks any ajustment for overtravel, tension or trigger pull, or the engagement of the trigger with the hammer.
As such, there exists a need for a trigger mechanisim that is easily installed in the AK-47 type rifle and its derivitives that easily replaces the original trigger. Such a device should be easily installed in the receiver of the rifle by removing the stock trigger mechanism and replacing it. Such a trigger mechanism should allow for easy adjustment of the over travel of the trigger, the engagement of the trigger with the hammer communicating with the firing pin, and the trigger pull force required to actually rotate the trigger to the firing position.
The device herein disclosed is an improved and adjustable trigger mechanism that is easily installed and submitted for the factory provided receiver mounted trigger mechanism in the AK-47 family of rifles. The operation of conventional AK-47 rifles is well known to those skilled in the art and need not be described in detail other than that such rifles control fire of the bullets from the cartridge using a trigger assembly that cooperatively engages with a hammer which communicates the firing action to the firing pin when released by the trigger mechanism. The hammer once released by the receiver mounted trigger mechanism rotates to causes the weapon to fire with the weapon then re-cocking the hammer using the power of the discharge to place it in position to fire again once the hammer is released.
The herein disclosed adjustable trigger assembly is manufactured to mount directly into the conventional receiver used to operatively engage the trigger assembly with the hammer in the AK-47 family of rifles. It is provided with a two-piece trigger assembly and can be used with the conventional hammer or in the preferred mode with a provided hammer which better cooperatively engages with the trigger assembly. It is best manufactured by machining the components from steel bar stock and in order to insure long and trouble free operation the components so manufactured are then heat treated and finished with black oxide. In a final step the parts are hand polished with special attention being made to the hammer and sear engagement areas to allow for a smooth trigger pull. When operatively assembled in place of the original trigger components mounted in the receiver, the disclosed device provides a major improvement in both the basic function of the trigger as well as the ability for multiple and minute adjustments to their operation to satisfy any marksmans concerns and desires. Both the finger-activated trigger and the disconnector pivot as a trigger assembly on the trigger pivot pin which mounts them both into the factory provided original receiver.
The trigger assembly composed of the engaged trigger and disconnector cooperatively engage with a hammer and provide a plurality of adjustment set screws which may be user adjusted to achieve the desired trigger adjustments. A first set screw provides for adjustment of the overtravel or free travel the trigger has once it has disengaged the factory provided hammer which fires the round. A second set screw adjusts the area of engagement of surface between the trigger and hammer thereby adjusting the amount of travel the trigger will have in the first stage of the two stage trigger operation. A third ajustment set screw adjusts the position of the disconnector in relation to the rotation of the trigger thereby determining whether the trigger has two stages of pull or a single stage of pull if so desired. Finally, a fourth adjustment set screw determines the tension of the internally mounted disconnector biasing spring away from the trigger and toward the hammer. If a two-stage trigger is selected, this adjustment provides a means to adjust the pull required in the second stage.
An object of this invention is the provision of an adjustable trigger mechanism for the AK-47 family of rifles, which is easily mounted into the factory-provided receiver to thereby substitute for the original non adjustable trigger.
Another object of this invention is the provision of a trigger mechanisim that is user adjustable for over travel.
An additional object of this invention is the provision of an adjustable trigger mechanism for the AK-47 family of rifles that provides for adjustment of the surface area of engagement between the hammer which fires the round in the chamber and trigger.
A further object of this invention is the provision of an adjustment for the disconnector component of the trigger assembly.
Yet another object of this invention is the provision of a tension adjustment for adjusting the pull required of the trigger to fire an AK-47 style of a rifle.
Still another object of this invention is the provision of multiple means of trigger adjustment that may be individually adjusted in relation to each other to yield a highly customizable trigger operation for the user.
Yet an additional object of this invention is the provision of such multiple adjustments of a trigger mechanisim to allow the user to choose a single stage or two stage trigger pull to discharge the rifle.
These together with other objects and advantages which will become subsequently apparent reside in the details of the construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout.